Inherited Change Chapter 16 Part 1

Homologous chromosomes Homologous chromosomes are matching pairs of chromosomes. In the original zygote, one of each pair came from the mother and one from the father. In humans, chromosome numbers 1-22 are called autosomes.

Sex chromosomes The non-matching X and Y chromosomes are the sex- determining chromosomes

Key terms Genes: Sequence of DNA that codes for protein. Alleles: A gene for a trait that exists in different forms Locus: The position on a chromosome where a gene is located (plural: loci) Diploid: When cells have two sets of chromosomes (2n) Haploid: When cells only contain one set of chromosomes like with gametes (n) Homozygous: having two identical alleles for a gene Heterozygous: having different alleles for a gene Genotype: The combination of allele for an organism Phenotype: The observable characteristics of an organism

Meiosis Meiosis 1 is reductive cell division as cells go from diploid to haploid (2n to n) Meiosis 2 is like mitosis Independent assortment and cross-over increase genetic diversity Independent assortment occurs during metaphase 1. Cross-over occurs between prophase 1 and metaphase 1. Cross over forms the chiasmata Cross-over leads to recombinant DNA

Meiosis

Gametogenesis - spermatogenesis Spermatogonia (mitosis - diploid) (meiosis) Primary spermatocyte (diploid) Secondary spermatocyte (haploid) Spermatid (haploid) Spermatozoan (mature sperm - haploid)

Gametogenesis - oogenesis Oogonia (embryo – diploid - mitosis) Primary oocyte (embryo – diploid – meiosis) Secondary oocyte (after puberty – haploid – meiosis) Ovum (after ovulation – haploid)

oogenesis

Parts of a flower Inside the anthers, diploid pollen mother cells divide by meiosis to make 4 haploid cells These cells mature into pollen grains Inside each ovule, a large, diploid, spore mother cell develops. Only one matures to become an embryo sac.

Structure of a flower

Genetic diagrams

Alleles Dominant: Allele that is expressed Recessive Allele that is NOT expressed

Codominance vs incomplete dominance

Sex linkage Sex linked genetic disorders such as hemophilia and Duchenne disease are caused by recessive alleles on the X chromosome.

Autosomal linkage When two genes are on the same locus on same autosomal chromosome

Dihybrid crosses Dihybrid crosses look at the inheritance of two genes at once.

Mutation Random Mutagen Transposon Base additions and base deletions usually have very significant effects on the structure and therefore the function of polypeptides. Frame shift Base substitutions often have no effect at all (silent mutation) Sickle cell anemia is an exception

Mutation

Gene control in prokaryotes Structural genes: Genes that code for proteins required by a cell. Regulatory genes: Genes that code for protein that regulate the expression of other genes. Repressible enzymes: The synthesis of a repressible enzyme can be prevented by binding a repressor protein to the operator on a bacteria’s DNA. Inducible enzymes: The synthesis of an inducible enzyme occurs only when its substrate (inducer)is present.

Operon An operon is a length of DNA making up a unit of gene expression in a bacterium. An operon consists of one or more genes and the control region that is recognized by the products of regulatory genes.

The lac operon The enzyme B-galactosidase hydrolysis the disaccharide lactose to glucose and galactose. (it breaks down the sugar in milk) E. coli bacteria makes B-galactosidase enzyme It must therefore regulate gene expression depending on the presence of lactose. It does this by the lac operon.

The lac operon The lac operon consists of the following: Structural genes lacZ – codes for B-galatosidase lacY – codes for permease (allows lactose in cell) lacA – codes for transacetylase Promoter region Operator region

lac operon

Gene control in eukaryotes Transcription factors (TF) The number of proteins that act as transcription factors increases the bigger the genome. Transcription factors control gene expression. General transcription factors make up protein complex that binds to promotor region Some TF activate genes in sequent for development A TF is responsible for sex determination in mammals TF allow responses to environmental stimuli (heat) Some TF control cell cycle and cell apoptosis (cell death) – tumor suppressor genes Hormones work through TF